Fig. 1.

Thirty-one tree-ring sites (red dots) in the middle-upper reaches of the YR. The thick blue line denotes the YR, and the thin blue line denotes the large tributaries along the river; blue triangles represent the gauge stations in the main channel, namely, Toudaoguai and Shanxian; the green shaded areas are irrigation districts. The map in the lower right corner shows the area of the Sanmenxia Reservoir.